Wire insulation



Dec. 21, 1954 J NOVAK 2,697,740

WIRE INSULATION Filed April 2, 1949 1721/2 11 for: .[Zadm' J,//0 W&Z

(2% orneg United States Patent WIRE INSULATION lzador J. Novak,Trumbull, Conn., assignor to Raybestos- Manhattan, Inc., Passaic, N. L,a corporation of New Jersey Application April 2, 1949, Serial No. 85,187

Claims. (Cl. 174-110) This invention relates to electrical conductors orother wire provided with an insulating wall or walls of novel character,and to a novel method for the manufacture thereof.

It is an object of the present invention to coat wire, such aselectrical conductors, welding wire, wire reinforced asbestos forpacking, wire for heat insulation, and the like with fibrous asbestos,but without requirement for such procedures as carding, spinning orweaving the asbestos fibers.

It is a further object to coat wire with asbestos in a rapid,economical, highly efiicient and efiFective manner, so as to provide theelectrical conductors. with a unitary insulating wall of fibrousasbestos of high thermal resistance and dielectric strength.

In general, the objects of the present invention are accomplished byextruding, in a continuous manner, an aqueous, plastic, self-sustainingmass of individualized and dispersed, i. e. non-clotted, asbestos fiberscomposed of single fibers or fascicular fiber bundles instead of thepredominantly clotted and tangled multiple fiber groups known to wet ordry asbestos practice, and wherein the fibers are in a lubricated,slippery and relatively slidable condition, and which may be prepared inaccordance with the general teachings of the ctr-pending application ofI. J. Novak, Serial No. 66,552, filed December 21, 1948, now Patent No.2,626,213, the present application being a continuation-in-part thereof.

The dispersed asbestos employed in the practice of the presentinvention, and as further described in said application, is composedpredominantly of Chrysotile asbestos fibers of unit diameter, that is ofa diameter of from about 200 to about 500 Angstrom units, the fibershaving organic surface-active agent adsorbed thereon, the aqueous phaseof the. plastic mass, as presently employed, containing an additionalrelatively small amount of free surface-active agent. As furtherdescribed and claimed in said application, the asbestos mass hereinemployed is prepared by mixing Chrysotile asbestos agglomerates with anaqueous liquid containing organic surface-active detergent adsorbable onthe asbestos and capable of forming n alkaline dispersion therewith. theamount of detergent being in excess of that adsorbed on the asbestos andsufficient to form and preserve the dispersion. One highly suitableexample of such detergent is Aerosol OT (dioctyl sodium sulfosuccinate).

By first preparing such dispersion in highly dilute condition, say 0.1%to 1% asbestos content it is possible to remove by, for example, slottedscreen plates such as employed in paper making, associated impurities,such as serpentine fragments, magnetite inclusions or other clots whichdo not open, or are not adequately opened, portions of original rock,and altered asbestos which is not amenable to fiberization. This resultsin a refined asbestos and, when ultimately applied to the wire. providesa covering of a fine uniform character with attendant advantages whichwill be readily apparent as to uniformity of insulating character,dielectric value, strength, etc., and allows extrusion of thin walls ofasbestos without the defects which might be caused by oversize fragmentsor clots of fiber.

For use in accordance with the present invention, the asbestosdispersion should have a high enough concentration or asbestos contentso as to beof a plastic, selfsupporting nature so that it will hold itsposition and shape when applied to the wire and not drip or drop ofi2,697,740 Patented Dec. 21,. 1954 between the period of application anddrying thereof. A dispersion of about 25% to 60% by weight of asbestoshas been found to meet this requirement where no additional viscositybuilders are added. By the use of viscosity builders such as glue,alginates, polyvinyl alcohol, bentonite, etc., the self-supportingcharacter may be obtained at lower asbestos concentrations. The maximumasbestos concentrations which can be employed is one which still hasadequate plastic flow and which will not clog the extrusion orifice, andboth the minimum and maximum concentrations will be related to thethickness of the extruded coating.

If the dispersion is originally prepared in dilute form, it may beconcentrated to the desired extent by removal of dispersing fluid bysuch means as filtration or centrifuging. Thus, an asbestos dispersionof about 30% fiber content prepared with Aerosol OT will be stable witha total Aerosol OT content of about 4% by weight of the asbestos, but,as: actually employed, will preferably contain about 6% thereof. Withhigher concentrations, the amount of dispersing agent will be some whatreduced, since although there is a minimum requirement for adsorption onand opening of the asbestos, an additional amount is required tomaintain the dispersion and which is proportional to the amount of theaqueous phase of the dispersion.

In one specific embodiment, and for the insulation of electricalconductor wires, particularly when little or no added binders areemployed, the present invention is further characterized by theemployment of asbestos fibers of spinning grade length which providesgood strength to the applied insulating wall and resistance to ruptureand deformation thereof in use and on fiexing, particularly when thefiber formation is arranged in helical fashion about the conductor, aswill be hereinafter more fully set forth. Fibers of spinning gradelength are those known as #1 and #2 crude, and the group of #3 grades ofmill fibers, in accordance with Canadian Chrysotile Classification, andas set forth on page 70 in Bulletin 403 of the U. S. Department ofinterior, Bureau of Mines, entitled Asbestos." The #3R grade has beenfound particularly suitable for the present purpose.

The invention will be further explained in connection with theaccompanying drawings, wherein:

Fig. 1 diagrammatically illustrates an arrangement of apparatus forextruding a plastic mass of dispersed asbestos upon an electricalconductor or other wire;

Fig. 2 is a view on the line 22 of Pig. 1; and

Fig. 3 is an illustration of a length of conductor, coated in accordancewith the present invention.

Referring to the drawings, the reference numeral 10 illustrates a hopperfor reception of a supply of a plastic mass of dispersed asbestos 11which is fed to the cham ber of the extruder 12 under pressure by meansof the mechanical feed screw 13. The dispersed asbestos mass may includeplastic binders in emulsion or in dissolved form, such as, for example,the binders previously indicated, rubber, silicone resins, or otherinsulating binders, compounding agents, fillers and the like, and whichdo not affect or upset the stability of the asbestos dispersion. Thesemay be added by direct addition to the plastic asbestos mass in asuitable mixer, such as a dough mixer, Banbury mixer, cake mixer, or thelike, as emulsions or cements, or even as undiluted oils or monomers,since the plastic asbestos mass has high emulsifying properties. Theelectrical conductor 14, which may be composed of one or more strands ofwire, is drawn from the reel 15 into the extrusion chamber 12, throughthe mandrel 16 and its wire aligning cone 17. Although not essential, ifdesired, the wire 14 may be preheated or pre-coated with an adhesive ofeither a water-aetivatable nature, such as glue, or heat-activatablenature, such as styrene polymer, for the purpose of providing betterbond of the asbestos to the wire. Although not shown, the extruder maybe provided with conventional means for heating the wire in its path toor at the extruding die 18 if the wire is to be pre-heated or providedwith a heat-activatable binder coating as previously indicated. As thewire is drawn through the orifice 19 of the extruding die 18, it becomessurrounded with a layer of dispersed asbestos 11 which, due to thedispersed, individualized nature of the fibers thereof and due to theextruding action, takes on a fiber formation which is substantiallyparallel in the longitudinal direction to the wire 14. Immediately uponissuance of the wire with its extruded wall of dispersed asbestos, it ispassed through the revolving head, generally indicated at 20, and whichcomprises a rotatable disc 21 provided with a plurality of radiallyadjustable arms 22 having rounded terminal ends for smoothing thecoating upon emergence from the extruder. tive rotary motion to theconductor and its coating, further serve to arrange the fibers of theasbestos coating in a helical direction as indicated at 23 of Fig. 3instead of permitting the fibers to remain directionalized in thedirection of the wire travel, so that the flexing of the coveredconductor will not tend to open up a path between the fibers to theconductor. For some uses, however, it may not be necessary or desirableto rearrange the fibers, and in such event the revolving head 20 may beby-passed. The covered conductor next passes through a suitable dryingand curing chamber 24 which may be electrically or otherwise heated, andis thereafter reeled up on the reel 25. The curing chamber serves toevaporate the moisture, and auxiliary solvent or other dispersing agentwhen present, from the dis-- persed asbestos coating and further servesto modify the character of the organic dispersing agent employed, and toreduce the unctuous or slippery and lubricated nature of the asbestosdispersion to a firm bonded character and to enhance the strengththereof. The drying or curing chamber 24 may further serve to heat-cureadmixed bonding agents when employed as previously indicated. Thetemperature and time of curing should be correlated and controlled so asto avoid steam blisters which might loosen the coating on the wire ordistort the coating within itself, and to dry or cure any of theaforementioned additives if employed, and activate a heat sensitiveadhesive on the wire if this is employed, as will be understood by thoseskilled in this art.

Although not illustrated, it will be apparent that a plurality ofsuccessive extrusion and curing means may be employed before reeling upthe coated wire on the reel 25, to coat the wire with a plurality oflayers of dispersed asbestos or other insulating or coatingcompositions. In similar manner, there may be interposed before finalreeling up of the wire, means for impregnating the asbestos coatingthecoating being amenable to such treatment, it being of a finely porousnature. Means may similarly be interposed or added, such as rolls orcondensing tubes, not shown, for densifying the dried or cured asbestoscoating, either as an intermediate step when successive layers areapplied, or as a final step.

Due to the nature of the asbestos dispersion employed, and the greatnumber of fibers of extremely small diameter, which predominate andcharacterize the material, the resulting coating is of high density andof high dielectric strength and yet withal may be composed substantiallyentirely of asbestos fibers, with the exception of the small residue oforganic material which may be as low as 1-2% after cure where no organicbinder has been added. Further, due to the employment of and the abilityto employ fibers of the spinning grade length, and the helicalizationthereof after extrusion, the resulting coating wall retains its unitaryor continuous The rotating arms 22, by their relaone-piece nature andstrongly clings to the wire upon repeated rough usage and flexing toprovide and maintain a highly effective insulating wall of a characterheretofore not obtainable.

In another, non-fully equivalent embodiment of my invention, I mayemploy shorter grade of asbestos, such as from the paper making gradesdown to dust for the coating of such wires as welding wire. With theseshorter fibers, however, a flexible or elastomeric heat resisting bindermust be incorporated, and I have found that I may employ such binders inthe amount up to 40% by weight of the short fiber asbestos, in whichevent the properties of the coating become predominantly the propertiesof the binder, rather than the properties of the asbestos. Such bindersas silicone binders, poly-fluoro ethylenes, orpoly-chloro-fluoro-ethylene may be used as binders. Since it isessential that the coating be of such a character that it resistsfracture at the knee on bending the covered wire, the flexible heatresistant binders should be incorporated in suflicient amount toovercome any tendency of short fiber asbestos to crack or break onbending to avoid exposure of the covered wire.

I claim as my invention:

1. The combination with a wire of a continuous surrounding layer of adried residue of a plastic mass comprised of an alkaline, gelatinous,stable, aqueous dispersion of individualized Chrysotile asbestos fiberspredominantly of a diameter of from about 200 to about 500 Angstromunits and containing organic surface-active agent adsorbable by andadsorbed on the fibers and a free excess in the aqueous phasemaintaining the dispersion.

2. The combination with a wire of a continuous flex-.

ible surrounding layer comprised of the dried residue of a colloidaldispersion os asbestos fibers.

3. The combination with an electrical conductor of a continuous,flexible, plastic surrounding layer comprised of the dried residue of acolloidal dispersion of asbestos fibers and a plastic binder.

4. The combination with an electrical conductor of a continuous,flexible surrounding layer comprised of the dried residue of a colloidaldispersion of asbestos fibers and an elastomeric binder.

5. An insulated conductor including a coating of asbestos which is theresidue of a dispersion of finely divided asbestos fibers in a liquid.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 290,121 Shaw Dec. 11, 1883 1,370,800 Egerton Mar. 8, 19211,907,616 Tucker May 9, 1933 1,946,331 Reeves Feb. 6, 1934 2,138,378Johnson Nov. 29, 1938 2,258,219 Rochow Oct. 7, 1941 2,308,638 BalthisJan. 19, 1943 2,332,535 Smith Oct. 26, 1943 FOREIGN PATENTS NumberCountry Date 544,681 Great Britain Apr. 23, 1942

5. AN INSULATED CONDUCTOR INCLUDING A COATING OF ASBESTOS WHICH IS THERESIDUE OF A DISPERSION OF FINELY DIVIDED ASBESTOS FIBERS IN A LIQUID.